[66bonne]

I'm running an E-brock Performer RPM on my 455. The intake has only one vac source which I use for power brakes and tranny take-off. I need to tap a vac source for positive crankcase ventilation. Should I tap into the intake runner or would it be better to tap into the plenum ?
Thanks for your suggestion/advise/recommendations.

Jim

[BVR421]

The factory tapped into 2 intake runners using a special long two port tube to draw from both sides of the dual plane intake. Idea was to get vac pulses for the pcv from the whole manifold. Doesnt the rpm have a plugged hole on the choke side of the plenum? Mine does but I dont know if its original
I would consider the big port at the back, I cant see how running everything off the same vac port would be a problem.
Most carbs have a 3/8 vac port on the backside of the basplate you could use for power brakes. ignition and accessories and use the one on the rpm for pcv?

Good job with your big old Cat, you got it flyin!

[misaac]

Jim, my Holley 830dp is the model without any vacuum ports so I added a 3/8" port at the back of the baseplate. I don't know what carb you are using but on mine there is a flat boss that would normally have a fitting so I drilled it and pipe threaded it for a 3/8" barb fitting. I put the PCV hose to this fitting so it would go to the whole manifold. For the power brakes, trans mod, and distributor, I used the port in #7 runner. I am using an RPM manifold and it only has 1 vacuum port. Suggestion to all of us junkyard hunters: Pick up as many oddball vacuum fittings in brass, steel, or pot-metal you can find. It is the kind of stuff never found in a typical jobbers brass assortment.

[66bonne]

BVR421-Unfortunately my RPM doesn't have a plugged hole, wish it did. I did try splicing the PCV line into the same vac port used for my brakes but evidently it drew too much vac away from the power brakes and trans modulator. Wouldn't stop and wouldn't shift !! And thanks for the props, trying to get this land barge to run a little faster.
Misaac-I'm getting ready to put on a Holley Dominator from Pro-Systems. It didn't come with a vac source on the carb altho' the base plate has a provision for tapping for vac.
But given what the carb cost I am hesitant to drill into it. The intake would be a lot cheaper to replace if I screw up. My thought was to tap into each side of the plenum for a vac source running to the valve cover. Or should I tap into a runner on each side ? Haven't done anything like this before so I thought I would ask.
Thanks, Jim

[Geoff]

Another way is to use a carb spacer if you have room. I have done this a few times. You may also pick up a few HP!!
Use a two hole spacer if you wish to maintain the RPM intake characteristics. A 3/4" spacer is best, but you could use 1/2" if you are careful. Drill & tap for a 1/8"NPT fitting to take a 3/8" hose. Remove the carb & turn it over. It should have a cutout section in the baseplate that connects both primary bores. You will need to drill a passage[s] to connect this carb passage with the PCV passage. I use a 1/4" drill bit, but 3/16" would probably suffice. This also makes for a neat set up, minimal hoses & fittings etc.

[66bonne]

Thanks for all the good ideas. I'm going to check for hood clearance today to see if I can run a 2" tall adapter. If there is enough clearance then I will tap into the adapter, easy enough.
However, if I don't have enough clearance then I'll have to use a low profile adapter and tap into the plenum or intake runners.
Thanks, Jim

[ponjohn]

Jim-

My rpm is the same as yours. I installed a vacuum source just to the DS of the crotch in the front. Not good, got runner pulsations and it would crack the rubber and make noise.

I installd the bung in the 1 inch carb spacer. Much better, now over the winter I need to have that hole welded up. Looks ugly with pipe plug in there.

john

[66bonne]

John - thanks for chiming in.
I may have come up with a solution. If I use a deep-drop air cleaner base and remove the 1" spacer currently on the manifold then I should have enough room for the 2" carb adapter. I'll just tap a vac source into the back of the adapter.
Wish me luck.
Thanks for the help, Jim